Moraxella catarrhalis is an important human respiratory tract pathogen. M. catarrhalis is the third most common cause of otitis media in infants and children, after Streptococcus pneumoniae and nontypeable Haemophilus influenzae, as documented in studies in which tympanocentesis has been used to establish the etiologic agent (Murphy, 1989, Pediatr. Infect. Dis. J. 8:S75-S77). M. catarrhalis is a common cause of sinusitis and conjunctivitis in both children and adults (See for example, Bluestone, 1986, Drugs 31:S132-S141; Brorson et al., 1976, Scand. J. Infect. Dis. 8:151-155; and Romberger et al., 1987, South. Med. J. 80:926-928); and is an important cause of lower respiratory tract infections in adults with chronic bronchitis and chronic obstructive pulmonary disease (Murphy et al., 1992, Am. Rev. Respir. Dis. 146:1067-1083; Catlin, 1990, Clin. Microbiol. Rev. 3:293-320). Additionally, M. catarrhalis can cause pneumonia, endocarditis, septicemia, and meningitis in immunocompromised hosts (Cocchi et al., 1968, Acta Paediatr. Scand. 57:451-3; Douer et al., 1977, Ann. Intern. Med. 86:116-119; McNeely et al., 1976, Am. Rev. Respir. Dis. 114:399-402).
Since recurrent otitis media is associated with substantial morbidity, and the attendant health care costs, there is interest in developing strategies for identifying and preventing these infections. One such approach is the development of vaccines for preventing bacterial otitis media. Besides infants and children benefitting from a vaccine to prevent otitis media caused by M. catarrhalis, adults with chronic obstructive pulmonary disease, and immunocompromised children and adults would benefit from a vaccine to prevent infections caused by M. catarrhalis. Outer membrane proteins are being investigated as antigens having utility in diagnosing and vaccinating against disease caused by bacterial pathogens, such as M. catarrhalis.
In an original typing scheme, eight major outer membrane proteins, designated by the letters A-H, were identified (Murphy et al., 1989, Microbial Pathogen. 6:159-174; Bartos et al., 1988, J. Infect. Dis. 158: 761-765). Further characterization of the outer membrane proteins of M. catarrhalis have added to this typing scheme. A protein having an apparent molecular mass of approximately 80 to 81 kilodaltons (kDa), as determined by sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE), has been described previously ("CopB protein": Helminen et al., 1993, J. Inf. Dis. 168:1194-201; "OMP B2 protein": Sethi et al., 1995, Infect. Immun., 63:1516-1520). CopB protein has been characterized as a surface-exposed, antigenically conserved protein that is a target for antibodies that enhance pulmonary clearance of M. catarrhalis in an experimental model of infection (Helminen et al., 1993, Infect. Immun. 61:2003-2010). Further, CopB may be involved in the serum resistance of M. catarrhalis in an infected host (Helminen et al., 1993, J. Inf. Dis. 168:1194-201).
Another outer membrane protein, B1, has recently been described. B1 protein was shown to be expressed in detectable amounts in the outer membrane of M. catarrhalis under iron-limiting conditions, i.e., expressed when the organism is growing in an iron-limited environment (Campagnari et al., 1994, Infect. Immun. 62:4909-4914). However, when the organism is grown in an iron-rich environment, the expression of the B1 protein becomes repressed. The B1 protein, having an apparent molecular mass of approximately 81 to 84 kilodaltons (kDa) as determined by SDS-PAGE, has been demonstrated to be distinct from the CopB (OMP B2) protein by differences in migration pattern in polyacrylamide gels, by antibody reactivity, and by expression in iron-limiting conditions (Campagnari et al., 1994, supra; and Campagnari et al., 1996, Infect. Immun. 64:3920-4). Further characterization of the B1 protein has demonstrated that it is a transferrin binding protein (Campagnari et al., 1996, supra). Several species of bacteria (e.g., Neisseria, Haemophilus, and Actinobacillus) have exhibited the ability to bind transferrin, and appear to use transferrin as a major iron source. For bacteria in general, there appears to be a correlation between virulence, and the ability to scavenge iron from the host.
Additional studies show that OMP B1 contains epitopes exposed at the surface of the bacterium expressing it, and that these surface-exposed epitopes are important antigens for the human humoral response to M. catarrhalis infection (Sethi et al., 1995, Infect. Immun. 63:1516-1520). More particularly, in several bronchiectatic patients tested, the major target of serum IgG against M. catarrhalis was B1 protein; and this observed immune response was consistently of high titer. Subsequently, it has been shown that patients with chronic obstructive pulmonary disease who have exacerbations due to M. catarrhalis, develop serum IgG and sputum IgA antibodies to B1 protein. Also children with otitis media have abundant antibodies to B1 protein in their convalescent sera (Campagnari et al., 1996 supra).
Properties of the B1 protein indicate that the gene encoding the B1 protein has utility in the diagnosis of and vaccination against diseases caused by bacterial pathogens, such as M. catarrhalis, that produce B1 protein or surface-exposed epitopes cross-reactive with B1 protein epitopes. Thus, it would be advantageous to provide for the identification, isolation, and purification of the gene encoding B1 protein for use as diagnostic reagents, for antigenic/immunogenic preparations such as vaccines, and for recombinant production of B1 protein.